(1) Field of the Invention
This invention relates to additives for lubricating oils having extreme pressure, antiwear and antioxidant properties. In one aspect, this invention is directed to additives for lubricating oils which are thiophosphorous, disymmetric bisulfides. As a further aspect, this invention relates to a process for the preparation of the additives as well as lubricating compositions containing such additives.
(2) Description of the Related Art
It is known to add additives to lubricating oils for improving the resistance to oxidation and wear of such oils. Thus, the zinc dialkyldithiophosphates such as those described in U.S. Pat. Nos. 4,436,400; 4,466,895; 4,587,062 and in Belgian Patent 896,226 have an antiwear and antioxidant effect. But those additives lose their effectiveness when the lubricated metal parts are subjected to high stresses. Therefore, they cannot be used as extreme-pressure additives. Besides, these metal salts in certain cases interact with the dispersants having a base of amines or polyamines thus altering the antiwear properties of the dithiophosphates. In addition, the presence of metals can lead to the appearance of ashes which counteracts the effect sought.
Unlike the above, another kind of additive, the polysulphurated olefins described, for example, in U.S. Pat. Nos. 4,097,387; 4,119,545; 4,119,550 and 4,198,305, can be used in conditions of extreme pressure. These products are good antiwear and extreme-pressure addditives, but they have no antioxidant effect.
An additive has now been found for lubricating oils which has at the same time, an antiwear, antioxidant and extreme-pressure effect.